EXECUTIVE SUMMARY

American National Standard Committee A58 periodically issues revisions to ANSI Standard

A58

"Building Code Requirements for Minimum Design Loads in Buildings and Other Structures."

This document defines magnitudes of dead, live, wind, snow and earthquake loads suitable

for inclusion in building codes and other regulatory documents.

The A58 Standard Committee

is a broad-spectrum group of professionals from the research community, building code

groups, industry, professional organizations and trade associations.

Their approval of a

proposed standard signifies that a consensus of those substantially concerned with its

scope and provisions has been reached, in that affected parties have had an opportunity to

comment on the standard prior to its implementation and opposing points of view have been

treated fairly.

The A58 Standard is concerned solely with structural load ings.

The specification of

specific allowable stresses or design strengths for materials of construction is outside

its scope.

The current version of the A58 Standard, ANSI A58.1-1972, is being revised,

with a tentative approval and publication date set for 1980.

This report addresses itself to changes to the A58 Standard which may occur subsequent

to the 1980 revision.

Its purpose is to develop a load criterion, including load factors

and load combinations, which would be suitable for limit states design with different

materials and methods of construction.

The current standard already contains a set of

load combinations and probability factors for allowable stress design.

This Executive

Summary is presented to review briefly the conclusions of the main report, giving an

overview of the recommendations and a concise rationale for their development.

Objectives:

1)

To recommend a methodology and set of load factors and corresponding load definitions

for use in the A58 Standard which would be appropriate for all types of building materials

(e.8., structural steel, reinforced and prestressed concrete, heavy timber, engineered

masonry, cold-formed steel, aluminum) and, in the future, for building foundations; and

2)

To provide a methodology for the various material specification groups to select

resistance factors (0) consistent with these load factors and their own specific objectives.

Rationale:

Structural design is a complex process involving iterative cycles of analyzing the

performance of idealized structures.

Each analysis cycle involves the checking of subassemblies, * members, components and connections against various limit states defined in a structural

specification dealing with the particular structural material.

Typically this checking

process involves satisfying a design criterion of the general form:

Factored Resistance > Effect of factored loads.

In the common case where the total load effect is a linear combination of individual loads,

In this formula the left side reflects the resistance (capacity) of the structural element

under consideration, and the right side denotes the forces which the element is expected

to support during its intended life (load effects).

The term R

n

is a nominal resistance

corresponding to a limit state (e.g., maximum moment which can be carried by a cross

section, buckling load, shear capacity), and is the "resistance factor," which is less

than unity and which reflects the degree of uncertainty associated with the determination

of the resistance.

The sum YQ is the product of the "load effect" Q (i.e., the force on

the member or the element

bending moment, shear force, torque, axial force

or the

stress on the component) due to the loading from different structural loads (e.g., dead

load, live load due to occupancy, wind load, snow load, earthquake load) and a load factor

Y, generally larger than unity, which accounts for the degree of uncertainty inherent in

the determination of the forces Q.

When nonlinearities in behavior are significant, the

load factor should be applied before performing the structural analysis.

In a more general sense or may represent a number of limit states (e.g., yielding

n

n

and tensile strength in a metal tension member) for each element, and ?

Yili reflects

i=1

the largest of several load combinations.

A substantial portion of this report is devoted

Using as an example a metal tension member,

and the tensile

where 0

are the resistance factors for the yield limit state, F. у

y' strength limit state, F. respectively, An is the net area, Dni In and W

A